We are measuring ligand binding sites on serum albumin by affinity labeling with bilirubin and fatty acids in an effort to more precisely define the properties of these sites. Refolding to form active sites after reduction of disulfide bonds is a second aspect of the study. Similar measurements, on a micro scale, will be applied to the albumin precursor, proalbumin, isolated from the rat, and to the circulating human proalbumin variant, Proalbumin Christchurch. The nature and site of the intracellular cleavage of proalbumin to form a albumin in rat liver are under study, using a microelectrophoretic technique with immunofixation to measure proalbumin.